(i) Field of the Invention
This invention relates to novel corrugated metal, e.g., steel, structural building panels. It is directed especially to those panels which, when assembled together, can provide a self-supporting, frameless building structure, preferably one in which the truss in hidden in the attic disposed between a ceiling of the building structure and its roof, and a "wide-span" roof, i.e., one which can have a wide span between supports.
(ii) Description of the Prior Art
In roofs having a wide span between supports, it is highly important that great rigidity and strength be provided in the building panels. It was thought that corrugated steel panels would be suitable for such purpose, but, in practice, it was found that such panels generally were not sufficiently rigid for the building of a "wide-span" roof. Moreover, the absence of a frame gave rise to other problems in proper designing of the roof panels.
A number of prior patents disclose complexly configured corrugated panels in an attempt to provide panels having great rigidity and strength. U.S. Design Pats. to Haman et al. No. 164,990 and Haman et al. No. 165,978 show the use of minor corrugations in valleys between major corrugations.
U.S. Design Pat. to Hield No. 178,605 shows the use of minor corrugations having cascades thereon in a valley between major corrugations.
Beech U.S. Pat. No. 2,585 also shows a corrugated metal panel with minor corrugations in the valleys between the major corrugations.
Sagendorph U.S. Pat. No. 362,118 shows a corrugated metal panel having a single minor corrugation on the major corrugations.
Sisson U.S. Pat. No. 1,800,363 shows (in FIG. 11) minor breaks in the hills and valleys of a corrugated panel.
Overholtz U.S. Pat. No. 2,073,706 shows minor corrugations in the valley between major corrugations having a minor corrugation thereon in a metal panel.
Ashman U.S. Pat. No. 2,417,899 shows a corrugated sheet having a minor corrugation in valleys between major corrugations, the major corrugations themselves having a minor corrugation thereon.
These panel constructions, as taught by the above-noted prior patents, however, have not been used and are not usable (indeed, they were not designed for use) for, or in, wide-span building constructions wherein the roof and wall panels are substantially self-supporting in mutual interconnection, i.e., for "wide-span" roof constructions.
One manner of attempting to solve such problem of providing panels for use in "wide-span" roof construction was suggested by Hermann in U.S. Pat. No. 2,812,730 patented Nov. 12, 1957. In that patent, building sheets were essentially elongated rectangular metallic sheets having an integrally formed bracing element in the form of a "V" along one edge of the sheet. The "V"-brace extended the full length of the sheet. It was suggested by Hermann that flat areas could be provided in these corrugations to give an even greater locking effect than would be achieved with overall curved or sine wave corrugations.
Another proposal was made by Behlen, in U.S. Pat. No. 3,064,771 patented Nov. 20, 1962, who provided a large span building covering unit in which deeply-formed or channel-ridged light gauge sheets were fastened together to form a unitary sheet metal plate to replace the upper chord of the conventional truss. Such structural units as taught by Behlen in this patent were said to provide structural building units of greater strength proportional to their weight than conventional construction and were said to be adapted to eliminate much of the dead-load of conventional construction, and were also said to be particularly adapted to eliminate parts used in conventional construction without eliminating the strength advantages of such parts.
Yet another proposal was suggested by Behlen, in U.S. Pat. No. 3,300,923 patented Jan. 31, 1967, which provided corrugated metal building panels which were curved lengthwise, so that they could be used to form a frameless building needing no roof supporting beams. In this Behlen patent, it was suggested that the presence of smaller corrugations within the large ones could greatly increase the possibility of forming a panel of a given gauge and a given depth of large corrugation to a given radius of curvature without buckling. Such a panel as proposed by Behlen having small lengthwise continuous corrugations in the larger corrugations was taught to have the combined corrugations of sufficient depth, contour and number and also the material of the panel should be of such strength and thickness, that when the panel was subjected to a compression load beyond the elastic limit of the material of which it was made, the panel would compress more easily than it would buckle.
Another proposal was provided by Behlen, in U.S. Pat. No. 3,492,765 patented Feb. 3, 1970, who provided corrugated wall and roof panels which had major and minor corrugations formed therein. The major and minor corrugations of the roof panels were in alignment with the major and minor corrugations in the wall panels.
A further proposal was provided by Cooper et al., in U.S. Pat. No. 3,308,596 patented Mar. 14, 1967, who provided a building wall and roof panel construction utilizing both major and minor corrugations, the panel having a symmetrical pattern of corrugations and permitting panel edge lap in such fashion that the panel assembly corrugation pattern was symmetric. The panel had both major and minor corrugations, the minor corrugations being continuous and being positioned on the major corrugations, the panel also optionally being fluted for control and removal of panel "oil canning", (the oil canning being fenced in by the minor corrugations, then limited areas are fluted).
Lacasse, in Canadian Pat. No. 978,322 patented Nov. 25, 1975, provided a corrugated building panel comprising two longitudinally extending major corrugations, each such corrugation being provided with a plurality of spaced-apart minor longitudinally extending continuous corrugations superimposed on the major corrugations and following the general corrugated pattern of the panel. The troughs an crests of the corrugations were flattened. In this way, each panel was provided with one central flat portion and a flat lateral side at each edge of the panel. By such construction, the load bearing capacity of the panel member was said to be increased.
While the corrugated steel building panels having continuous minor corrugations superposed in major corrugations provided by Hermann, U.S. Pat. No. 2,812,730; Behlen, U.S. Pat. No. 3,064,771; Behlen, U.S. Pat. No. 3,300,923; Behlen, U.S. Pat. No. 3,492,765; Cooper, U.S. Pat. No. 3,308,596; and Lacasse, Canadian Pat. No. 978,322, were considerably stronger on a weight/weight basis than other corrugated panels, it was discovered that such panels were, nevertheless, subject to local buckling. Thus, it has been found that the corrugated steel building panel buckled within the minor corrugations, i.e., was subject to local buckling, when subjected to a load which was less than the theoretical maximum load which it should support on the basis of the weight of steel used. Thus, the local buckling factor (Q) (a measure of the degree to which the strength approaches the theoretical maximum) was as follows for a panel based on that taught in the Lacasse Canadian patent:
TABLE I ______________________________________ Gauge Q ______________________________________ 22 0.62 20 0.63 18 0.74 16 0.81 14 0.87 ______________________________________
In order for the minor corrugations on the major corrugation to provide a maximum strength improvement, the local buckling factor (Q) should approach 1.0. It will be seen from this table that Q ranged from 87% maximum (for thick steel) to 63% maximum (for thin steel).